Let’s think outside the box. It looks to me like the hinge consists of 2 bars of mild steel measuring about 150m x 20mm x 3mm. One bar has an ‘S’ shape at the end. They are joined by some sort of pivot assembly which must be rust-resistant.
I think the same effect could be obtained by implanting a skateboard bearing on each rail holding the rungs. It would be retained by a metal cover. Then a simple axle could be placed on the back rail to which it is joined.
I bought a pair of 200mm (8″) Trestle Joint Hinge from EBay and noticed that the angle was 42 degrees. This is much bigger that the 30 degrees that Paul modified to 38 degrees in his video.
I am wondering if I should modify the ladder to 42 degrees or just adjust the hinge on the front legs which seem to have a lot of space. Of course then the angle of the hinge would not parallel the leg which would just seem to be an aesthetic issue. Suggestions and/or comments?